1. Field of the Invention
The present invention relates to a surface wave motor built-in lens barrel for moving a photographing lens by use of a surface wave motor.
2. Related Background Art
This type of known surface wave motor built-in lens barrel has hitherto been constructed such that a manual operation member and a fixed member of a surface wave motor are so integrally connected as to be rotatable with respect to a fixed drum, and a mode selecting member involves the use of only an electric switch.
In this lens barrel, when a manual focus adjusting mode is selected by a mode selecting member, the moving member and the fixed member of the surface wave motor become integral and are rotated interlocking with a manual operation of the manual operation member, thereby moving a photographing optical system. Further, when an autofocus adjusting mode is selected, the fixed member is fixed to the fixed drum, and the photographing optical system is moved with a rotation of the moving member.
With this construction, the photographing optical system can be moved without damaging a contact surface between the moving member and the fixed member of the surface wave motor in the manual focus adjusting mode.
FIG. 2 is a sectional view illustrating a prior art example (e.g., Japanese Patent Application Laid-Open No. 4-343310) of the surface wave motor built-in lens barrel. FIG. 3 is a cross-sectional view illustrating a power supply portion in FIG. 2. FIG. 4 is a schematic block diagram of the lens barrel in the prior art example.
FIG. 2 shows a state of the autofocus adjusting mode in which focus adjusting optical systems L2, L3 are moved by a rotating force of the surface wave motor. In this state, a mode changeover switch 20 is set in the autofocus adjusting mode.
The focus adjusting optical systems L2, L3 are held by the lens holding drum 2 and moved in the optical-axis direction, thus adjusting a focal point. The lens holding drum 2 is so fitted to an inner periphery of a central intermediate-diameter portion 1a of the fixed drum 1 as to be movable in the optical-axis direction. A pin 3 is embedded in an outer peripheral part of the lens holding drum 2 and penetrates a guide groove parallel to the optical axis, which is formed in the central intermediate-diameter portion 1a of the fixed drum 1. The tip of the pin 3 engages with a cam groove 4a formed in an inner peripheral surface of a cam ring 4.
The cam ring 4 is fitted to an outer peripheral part of the central intermediate-diameter portion 1a of the fixed drum 1, and a pin 5 embedded in the outer peripheral part of the central intermediate-diameter portion 1a engages with a circumferential groove formed in the inner peripheral surface of the cam ring 4. Hence, the cam ring 4 is unmovable in the optical-axis direction but rotatable through only a predetermined angle about the optical axis. Further, a distance scale is indicated on a rightward large-diameter outer peripheral portion 4c of the cam ring 4.
A fixing member 6 of a surface wave motor is so attached to the outer peripheral part of the central small-diameter portion 1c of the fixed drum 1 as to be rotatable about the optical axis. A window member 8 is formed in the large-diameter portion 1d of the fixed drum 1 and is formed of a transparent synthetic resin. It is possible to read the distance scale indicated on the rightward large-diameter outer peripheral portion 4c of the cam ring 4 through this window member 8 as well as through an intermediate ring 7 formed of the transparent synthetic resin.
A rotator 9 comes into frictional contact with the fixing member 6 and is so provided as to be rotatable with respect to the fixing member 6 through a bearing 12. An engagement groove 9a is formed in a left part of the rotator 9 and engages with an engagement protrusion 4d provided on a rightward large-diameter inner peripheral part of the cam ring 4. Therefore, the rotator 9 and the cam ring 4 rotate integrally in the rotating direction. Further, a biasing member 14 causes the fixing member 6 and the rotator 9 to come into frictional contact with each other through a disk 13.
A manual operation ring 10 is fitted respectively to the leftward large-diameter portion 1e and the large-diameter portion 1d of the fixed drum 1. The intermediate ring 7 composed of the transparent synthetic resin is rotatably provided along the inner peripheral part of the manual operation ring 10.
A glass epoxy plate 15 is fixed to the fixing member 6 and includes, as illustrated in FIG. 3, a conductor portion 15a extending over the entire periphery of the ring. With this arrangement, even when a brush 16 slides on the conductor portion 15a and the fixing member 6 is in any angular position, an electrical connection to the fixing member 6 can be attained. Note that the glass epoxy plate 15 is formed with a through-hole 15b in an offset position from a ring-like portion. The conductor portion 15a conducts to a conductor portion provided on the rear surface of the glass epoxy plate 15 and electrically connected to the fixing member 6 from this rear surface.
A presser plate 17 is a plate for fixing the brush 16 to a brush fixing plate 18. The brush fixing plate 18 is fixed to the fixed drum 1 with a small screw 19.
A mode changeover switch 20 is slidably provided on the fixed drum 1 is set in a manual focus adjusting mode when slid in a direction M in FIG. 2 but in an autofocus adjusting mode when slid in a direction A. Further, the mode changeover switch 20 is constructed to generate electric signals corresponding to the respective modes.
A changeover plate 21 is fixed to a mode changeover switch with a small screw 23. A plate spring 22 is fixed to the fixed drum 1 with a small screw 24. The plate spring 22 is possible of engaging with and disengaging from a plurality of engagement grooves 6a formed in the outer peripheral part of the fixing member 6.
When the mode changeover switch 20 is slid in the direction M, that is, when in the manual focus adjusting mode, the changeover plate 21 simultaneously moves, and the plate spring 22 is pushed up as indicated by a dotted line in FIG. 2, thus making the plate spring 22 separate from the engagement grooves 6a. In a state where the plate spring 22 disengages from the engagement grooves 6a of the fixing member 6, the manual operation ring 10 is rotatable.
When the mode changeover switch 20 slides in the direction A, that is when changed over to autofocus adjusting mode from the manual focus adjusting mode, the changeover plate 21 simultaneously moves, and the plate spring 22 is, as indicated by a solid line in FIG. 1, returned to an initial state. Then, the plate spring 22 engages with the engagement grooves 6a of the fixing member 6, thereby hindering the rotation of the manual operation ring 10.
Note that there is to be satisfied such a condition as C&lt;B&lt;A, where A is a frictional torque of between the fixing member 6 and the rotator 9, B is a frictional torque between the fixed drum 1 and the fixing member 6, and C is a torque required for driving the lens holding drum 2.
(Explanation of Autofocus Adjusting Mode)
Next, the operation of the prior art lens barrel will be explained with reference to FIG. 2.
When in the autofocus adjusting mode, the mode changeover switch 20 is in a position A and, as indicated by the solid line in FIG. 2, the plate spring 22 engages with the engagement grooves 6a of the fixing member 6. Hence, the rotation of the manual operation ring 10 is hindered, and the fixing member 6 is also in an impossible-of-rotation state.
Herein, when the surface wave motor is supplied with the electricity from an unillustrated control mechanism (corresponding to a power supply in FIG. 4), surface traveling waves are produced on the fixing member 6, and the rotator 9 rotates in the circumferential direction. When the rotator 9 rotates, the engagement protrusion 4d provided on the cam ring 4 engages with the engagement groove 9a formed in the left part of the rotator 9, and consequently the rotator 9 and the cam ring 4 integrally rotate. Then, when the cam ring 4 rotates, the lens holding drum 2 moves along the optical axis, thus performing the autofocus adjustment.
(Explanation of Manual Focus Adjustment)
When in the manual focus adjustment mode, the mode changeover switch 20 is slid in the direction M in FIG. 2. The supply of the electricity to the surface wave motor is thereby cut off.
When the mode changeover switch 20 is slid in the direction M, the changeover plate 21 fixed to the mode changeover switch 20 also simultaneously moves, and the plate spring 22 fixed to the fixed drum 1 is pushed up and consequently disengaged from the engagement groove 6a formed in the outer peripheral part of the fixing member 6.
In a state where the plate spring 22 disengages from the engagement groove 6a, the manual operation ring 10 is rotatable, and, besides, since the supply of the electricity to the surface wave motor is cut off, the surface wave motor can not be driven. The fixing member 6 and the rotator 9 are in such a state that these two members are strongly pressed by the biasing member 14.
Further, there is met such a condition as C&lt;A, where the A is the frictional torque between the fixing member 6 and the rotator 9, and the C is the torque needed for driving the lens holding drum 2. Hence, when rotating the manual operation ring 10, the fixing member 6 and the rotator 9 integrally rotate through the intermediate ring 7.
When the rotator 9 is rotated, the engagement protrusion 4d provided on the cam ring 4 engages with the engagement groove 9a formed in the left edge part of the rotator 9, and, therefore, the rotator 9 and the cam ring 4 integrally rotate. When the cam ring 4 rotates, the lens holding drum 2 moves in the optical-axis direction, thereby performing the manual focus adjustment.
According to the prior art example, when in the autofocus adjustment mode, the mode changeover switch 20 is in the position A, and, as illustrated in FIG. 2, the plate spring 22 engages with the engagement groove 6a formed in the outer peripheral part of the fixing member 6. Consequently, the manual operation ring 10 is hindered from rotating, and the fixing member is also in the impossible-of-rotation state.
Even when the plate spring 22 does not engage with the engagement groove 6a, however, there is satisfied such a condition as C&lt;B, where the B is the frictional torque between the fixed drum 1 and the fixing member 6, and C is the torque necessary for driving the lens holding drum 2. Hence, not the fixing member 6 but only the rotator 9 rotates. That is, the mode can be simply changed over to the autofocus adjustment mode and the manual focus adjustment mode, depending on whether or not the surface wave motor is supplied with the electricity.
Accordingly, there is no necessity for the mechanical changeover when performing a go-home photographing function of memorizing an arbitrary photographing distance beforehand and, after taking a shot at another photographing distance, moving the lens to the memorized photographing distance and also a manual focus adjustment mode priority photography of instantaneously changing over the mode to the manual focus adjustment mode by rotating the manual operation ring during the photography in the autofocus adjustment mode. Hence, it is quite easy to incorporate the mechanism for quickly performing the above function and changing over the mode.
The above-mentioned surface wave motor has such an aspect that characteristics of the number of rotations and the output torque of the moving member are substantially determined by a size or a shape of the motor. For example, if the torque required for moving the photographing optical system is determined, the number of rotations is automatically determined. Accordingly, if a time needed for the photographing optical system to move from a photographing distance .infin. position to a closest position is determined, it follows that there is automatically determined an angle necessary for the moving member to rotate from the photographing distance .infin. position to the closest position.
In the above-described conventional lens barrel, however, when selecting the manual focus adjustment mode, the fixed member and the moving member of the surface wave motor become integral and rotate interlocking with the manual operation of the manual operation member, thus moving the photographing optical system, resulting in a determination of the angle needed for the rotation of the manual operation member from the photographing distance .infin. position to the closest position. Accordingly, if this angle is too small to make the manual focus adjustment, there arises such a problem that the manual focus micro-adjustment is impossible.
Under such circumstances, for the purpose of obviating the above problem, the present applicant proposed a surface wave motor built-in lens barrel disclosed in Japanese Patent Application No. 6-249224, which is capable of performing the manual focus micro-adjustment by setting the angle needed for the rotation of the manual operation member from the photographing distance .infin. position to the closest position larger than an angle of rotation of the moving member of the surface wave motor.
More specifically, the lens barrel includes an angle-of-rotation enlarging device constructed of a plurality of rollers rotatably provided at a part of the fixing member and rotating on the side surface of the fixed drum and a biasing member for bringing the manual operation ring into the frictional contact with the inner peripheral surface of the fixed drum through the rollers by pressing it against that inner peripheral surface. A ratio of an angle of rotation of the manual operation ring to that of the fixing member is enlarged to 2:1.
In the above-mentioned conventional lens barrel and the lens barrel disposed in Japanese Patent Application No. 6-249224, however, the rotary force applied on the manual operation ring in the manual focus adjusting mode is transferred directly to the fixing member via the intermediate ring 7 (and the angle-of-rotation enlarging device). Consequently, the fixing member elastically deforms, and this deformation extends up to a contact surface with the rotator. Herein, the surface wave motor drives the rotator by use of traveling waves having an amplitude on the order of 1 .mu.m that are generated by the fixing member. Accordingly, there exists a problem in which a slight deformation on the contact surface between the fixing member and the rotator might be a cause of decreasing an electromechanical energy conversion efficiency of the surface wave motor.